Method of pumping viscous crude



April 30, 1968 c. D. M AULIFFE E 3,380,531

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ATTORNEYS April 30, 1968 c D, c F r- ET AL 3,380,531

METHOD OF PUMPING VISCOUS CRUDE Filed May 18, 1967 4 Sheets-Sheet 5CAUSTIC SOLUTION STORAGE EMULSION STORAGE INVENTORS CLAYTON D. MCAUL/FFERALPH SIMON CARL E. JOHNSON, J.

ATTORNEYS United States Patent 3,380,531 METHOD OF PUMPING VESCOUS CRUDEClayton D. McAulitie, Fullerton, Ralph Simon, Whittier,

and Carl E. Johnson, Jr., Laguna Beach, Calitl, assignors to ChevronResearch Company, San Francisco, Calif., a corporation of DelawareContinuation-in-part of application Ser. No. 503,210,

Oct. 23, 1965. This application May 18, 1967, Ser.

No. 642,284 i 16 Claims. (Cl. 166-45) ABSTRACT OF THE DISCLOSURE Theinvention is directed to improving the pumpability of crude oil from awell by forming a low viscosity oil-in-water emulsion near the pump inthe well.

This application is a continuation-in-part of Ser. No. 503,210 filedOct. 23, 1965, and now abandoned.

The present invention relates to a method of pumping viscous crude oil.More particularly, it relates to a method of pumping viscous crude bycausing an oil-inwater emulsion of said crude to be formed at a pointadjacent the actuating element of a downhole pump and then pumping saidemulsion having a substantially lower viscosity than the native oil fromthe well bore.

Viscosity frequently limits the rate crude oil can be produced from awell. For example, in wells that are pumped by a sucker rod string,viscous drag by the crude oil on the string slows its free fall bygravity on the downstroke. On the upstroke, this drag also slows thestring, decreases oil flow through the production tubing, and increasesthe power required to raise oil and rod string. In some instances wherethe oil is highly viscous, such as the Boscan field in Venezuela, thestrength of the sucker rods limits the depth at which the pump can beoperated. Alternatively, hydraulic pumps can be placed at the bottom ofthe well, but they must still overcome the high viscous drag thatrequires high power oil pressures and high pump horsepower.

The downhole pump usually provides the pressure required to pump theproduced oil from the wellhead to surface gathering tanks. Whereviscosity is high, this may require the use of extra strength wellheadequipment (packings, gaskets, heavy walled pipes and the like) towithstand the pressures required to move such viscous oil from wellheadto storage tank.

It has been proposed heretofore to reduce the viscosity of heavy crudeoils prior to pumping by introducing low viscosity crude oils, whiteoil, kerosene or the like into the well bore to dilute or thin theproduced crude. In rod pumped wells, it is common to surround the suckerrod string with an extra tubing. Low viscosity oil is pumped down thistubing so that the string is surrounded by lower viscosity oil. Thisadded light oil then mixes with the viscous crude near the travelingvalve of the pump to lighten and thin the column of crude oil beingpumped from the well through the annulus formed by the inner and theproduction tubings of the well. Alternatively, low viscosity oil can bepumped down hollow sucker rods and the diluted crude oil producedthrough the annulus between the hollow rod string and the tubing.

As noted above, wells are also frequently pumped by downhole hydraulicunits. In these wells at low viscosity oil is used as a power fluid.Frequently it is also mixed with the crude under production. In such asystem it is common to reclaim the lower viscosity or high gravity icecomponents from the mixed, produced fluid for reuse as the power oil.However, in some wells the native crude contains so little low viscositycomponents that it is necessary to import oil from other sources for useas the power fluid. Economically, this may make it necessary to use aclosed hydraulic system. To operate as a closed system, the downholehydraulic pump is connected to the surface by two pipes to supply andreturn the power oil and thereby prevent it from commingling with thecrude. Obviously, the viscosity of the produced crude is not reduced bythe power oil and great hydraulic power is required to lift the crude.

None of the above described systems greatly reduces the viscosity of thenative crude oil, unless excessive volumes of the high gravity fluidsare used. Furthermore, it is expensive to reclaim the less viscous oiladded to the produced crude.

In accordance withthe present invention, it is a pri mary object toreduce the power required to pump high viscosity crude down to valuesthat are substantially the same as that required to pump water, and atthe same time, reduce the cost of extracting the viscous crude oil fromthe produced fluid on stream.

Broadly, the invention has to do with a process of increasing thepumpability of a viscous crude pumped from a well bore by means of adownhole pump in said well here, which comprises forming adjacent saiddownhole pump an oil-in-water emulsion of the viscous crude, saidemulsion having a substantially lower viscosity than the unemulsifiedcrude, and pumping the oil-in-water emulsion to the surface of theground.

in one aspect, the invention provides a method of increasing the rate ofpumping a viscous crude from a well bore provided with a downhole pump,which method involves contacting the crude adjacent the pump with waterand a base, in the presence of an emulsifying agent for said viscouscrude, emulsifying the crude to form an oilin-water emulsion, andpumping the oil-in-water emulsion from the well bore to the surface. Theamount of water introduced by the basic solution and any connate waterpresent with the oil are suflicient to produce an oil-in-water emulsionhaving a substantially lower viscosity than the unemulsified crude oil.In general, the oil-in-water emulsion contains, by volume, about 50 tooil and 30 to 50% water, based on the emulsion. The amount of base usedis such that the emulsion has a pH in about the range 8 to 13.8,preferably around 9 to 10. pH of emulsion being produced can bedetermined continuously or intermittently by known means, such ascontinuously recording pH meters, and Universal pH indicator paper. Theviscosity of the emulsion can be varied by adjusting its water content,the viscosity being lowered with increase in water content, andincreased by raising the oil content.

The invention is particularly useful when applied to asphaltic crudes,for example, the heavy California crude oils, Which upon contact andagitation wit-h an aqueous basic solution are converted into anoil-in-water emulsion. Accordingly, we have found that the viscosity ofthe produced stream can be reduced by a factor of to 1000 that of theoriginal viscous asphaltic crude by introducing into the well adjacentthe pump, or the actuating element thereof, an aqueous solution of abase, for example, sodium hydroxide, to react with the saponifiableconstituents of the crude to produce an emulsifying agent in situ. Thebasic solution is injected through a flow line whose outlet in the wellbore is below the intake of the downhole pump so that agitation of theoil and alkaline solution by the pump creates the required oil-in-wateremulsion. As hereinabove mentioned the amount and concentration of thebase solution to be injected is such as to neutralize the acidiccomponents of the oil to a pH in the range 8 to 13.8, preferably 9 to10, to produce an emulsion containing about 50 to 70% oil and 50 to 30%water, by volume, based on the emulsion. Obviously, the solution of thebase to be added will vary in amount and concentration depending on thecrude to be emulsified and the amount of connate water. Thus from verydilute solutions, less than 0.1%, to very strong solutions, up to 50%,will be used depending on acidic constituents of the oil and the connatewater.

The base in forming the aqueous alkaline solution can be an alkali metalhydroxide, such as sodium hydroxide, potassium hydroxide, and lithiumhydroxide, or ammonium hydroxide. Other inorganic basic materials, suchas sodium phosphate, sodium metasilicate, sodium carbonate, can be used.In addition to the inorganic bases, it is also possible to use strongorganic bases such as the amines, for example, ethylamine, propylamine,triethanolamine, thus forming emulsifying amine soaps with the acidcontained in the asphaltic crude. Generally, it is preferred to use analkali metal hydroxide or ammonium hydroxide, and more preferably, acaustic solution formed of sodium hydroxide. However, the particularbase will be selected on the basis of price and availability at the oilfield where the viscous crude is to be produced.

As hereinabove mentioned, the invention is particularly useful whenapplied to asphaltic crudes that contain saponifiable constituentscapable of forming with the base solution the effective emulsifyingagent required in forming the oil-in-water emulsion. Examples of suchcrude oils are the naphthenic-base crude oils such as the heavyCalifornia crude oils, for example, those of Kern County, Coalinga, theValley crudes, and the coastal crudes (Santa Maria); the heavyVenezuelan crudes, for example, Boscan, Tar Zone crude oils; the heavyMexican crude oils, for example, the Ebano and Panuco types; the heavycrude oils of the Texas Gulf Coast area; the asphalt-containing crudesin Mississippi; the naphthenic oils from the Mid-Continent fields; theintermediate 'base oils, such as those of Kuwait, Iran, Bahrein, Iraq;and the Arabian crude oils.

Various crude oils have different susceptibilities to form the desiredoil-in-water emulsions required to obtain the benefit of the presentinvention. Specifically, it is desirable to evaluate the crude oil forits ability to form the desired emulsion prior to injecting sodiumhydroxide or other alkali metal hydroxide solution into a crudeproducing well to form the prescribed oil-in-water emulsion. In general,the amount of alkali metal hydroxide, such as sodium hydroxide, to beinjected will be such that its concentration, expressed in normality,will have a value falling between 0.002 N and 0.75 N, based on totalWater present before emulsification, that is, the water not onlycontributed by the alkaline solution but also any connate water presentwith the oil to be emulsified. Generally, the emulsions are most readilyformed by crude oils having high acid numbers. The emulsion is also moreeasily formed with fresh waters whose salt content is low. If the nativeor connate water from the formations producing oil has a salt contentsuch as to interfere with the formation of the emulsion, the problem canbe overcome by supplying greater quantities of fresh water from thesurface or additional preformed emulsifying agent.

The following table illustrates efiective ranges of sodium hydroxide inweight percent concentration in the aqueous phase that have been used toemulsify samples of crude oil to form oil-in-water emulsions. Thediscontinuous oil phase was maintained at about 70%, by volume, toproduce oil-in-Water emulsions from the crude oils over the givenpreferred ranges.

NaOH Conc.,

Crude oil: weight percentage in Water Midway-Sunset A 0.41.4Midway-Sunset B 0.050.5 Midway-Sunset C (ll-1.0 West Coalinga A 0.05l.0West Coalinga B 0.1-0.5 Boscan 0.050.3 Casmalia 0.10.6 Cat Canyon0.1-l.0

There are certain oil-bearing formations in which the formation waterhas a sufficiently high alkali metal carbonate content to permitformation of alkali metal hydroxide in situ by injecting an alkalineearth metal hydroxide, such as calcium hydroxide, a relatively lessexpensive alkaline material, which reacts with the formation water toform insoluble alkaline earth metal carbonate and aqueous alkali metalhydroxide.

For example, in the Boscan field in Venezuela, formation water has ahigh sodium bicarbonate content, calcium hydroxide is locally availableand inexpensive, while sodium hydroxide must be imported. The inventioncan be practiced in the Boscan field by injecting either a saturatedsolution of calcium hydroxide or a dilute dispersion of solid calciumhydroxide in water into the borehole adjacent the downhole pump, thereto react with the formation water forming calcium carbonate precipitateand dilute aqueous sodium hydroxide which causes the formation of anoil-in-Water emulsion pursuant to the invention.

Alternatively, with connate waters that do not contain the alkali metalbicarbonate, such as sodium bicarbonate, we have found that theoil-in-water emulsion can be formed by adding sodium carbonate Na (COalong with calcium hydroxide to precipitate the calcium ion as solidcalcium carbonate and form the dilute aqueous sodium hydroxide solution.The basic solution then forms the oil-in-water emulsion required toobtain the advantage of the present invention. It is also advantageouswith waters that contain calcium or magnesium salts to add sodiumcarbonate along with the alkali metal hydroxide to form calciumcarbonate or magnesium hydroxide. Even when these compounds do not forma precipitate, they are sufficiently inactivated so that they do notinterfere with the reaction of the basic solution with the crude to forman oil-in-water emulsion.

With non-asphaltic crudes, for example, Minas and Red Wash crudes, thatare nevertheless viscous because of a high paraffin content but containlittle, if any, saponifia-ble material, it is possible to form therequired oil-in-water emulsion downhole by injecting preformedemulsifying agent together with sufiicient alkaline solution to maintainthe specified concentration of base. A suitable emulsifying agent can beobtained in known fashion by caustic extraction of certain low-gravityaspaltic crudes, such as those produced from numerous formations inCalifornia oil fields, for example, Casmalia, San Ardo, Midway-Sunset,West Coalinga, and Poso Creek.

A good source of saponifiable materials suitable for making theemulsifying agent are naphthenic acids, having for example, an averagemolecular weight in about the range 300700. These are obtainablecommercially, and can be introduced downhole along with the aqueousalkaline solution, the latter being of sufiicient concentration andamount to provide the specified alkaline content and to form theemulsion having the desired composition, If need be Where thesaponifiable materials are insoluble in the alkaline solution, they canbe present in the form of a dispersion in oil, for example, oil of likecharacter to be recoverd.

Desirably the resulting low-viscosity oil-in-water emulsion is theneither pumped to a storage tank or into a pipeline. The emulsion maythereafter be broken by the addition of acids, such as hydrochloric,sulfuric or carbonic, in a concentration equivalentto the amount ofhydroxyl ion added. The water can be separated from the oil by passingit through a heater treater, or electric dehydrator. If required,emulsion breakers, for example such salts as ammonium chloride, sodiumchloride or calcium chloride may be added to produce complete breakingof the oil-in-water emulsion.

In another aspect, the invention provides a method of improving thepumpability of crude from a well by forming an oil-in-water emulsion inthe well by mixing with the oil an aqueous solution containing anonionic surfactant. In many instances it is possible to utilize theconnate water already present in the well and form the oilin-wateremulsion by injecting a nonionic surfactant down the well. This form ofthe invention is especially useful when the connate water has arelatively high salt content.

The oil-in-water emulsion which is formed by mixing the nonionicsurfactant solution and the oil in a well adjacent a downhole pump isrelatively stable while the mixture is being moved. The mixture tends toseparate into a separate oil phase and a separate water phase when leftstanding and therefore the mixture can be easily broken down intoseparate oil and water phases.

The oil-in-water emulsion may be formed with as little as surfactantsolution. It is preferred, however, to have substantially moresurfactant solution present in the well when forming the emulsion. A /50ratio of surfactant solution and oil has given good results.

An aqueous surfactant solution is added to the oil to form the desiredmixture. As indicated, the amount of water may be as little as about 15percent. The surfactant is added to the water before the water is mixedwith the oil. Nonionic surfactants useful in the present invention canbe divided into five basic types by linkage. (See Emulsion Theory andPractice, by P. Becher, ACS Monograph, No. 162, 1965, ReinholdPublishers, New York.) These five types are ether linkage, esterlinkage, amide linkage, miscellaneous linkage and multiple linkage.

Further objects and advantages of the present invention will becomeapparent from the following detailed description, includingexemplification of the invention applied to viscous crude oils, taken inconjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic, vertical sectional view of one form ofapparatus suitable for practice of the method of this invention andrepresents schematically .a system for controlling operation of a wellhaving a sucker rod actuated downhole pump.

FIGURE 2 is an enlarged cross-sectional view of a part of the downholeapparatus shown in FIGURE 1, particularly illustrating operation of thepump on the downstroke.

FIGURE 3 is a view similar to FIGURE 2 showing the pump on the upstroke.

FIGURE 4 is a vertical sectional view of a downhole hydraulic pumpingsystem using the method of this invention, and illustratingschematically the surface operating equipment associated therewith.

FIGURES 5 and 6, respectively, indicate the down stroke and upstroke ofthe operating unit of FIGURE 4, showing in greater detail use of anaqueous caustic solution as the power fluid and its mixture with thecrude oil at the intake of the pump unit.

The method of the present invention is illustrated in FIGURE 1 by a rodactuated downhole pump unit 24 equipped to dilute the production crudewith a high gravity (low viscosity) oil. Eadie Patent 2,672,815 isrepresentative of the prior art. As particularly distinguished from theprior art, the present invention permits reducing the viscosity of thepumped fluid to just about that of water. This reduced viscosity isachieved by injecting an aqueous solution of a base, hereinaftertypified by sodium hydroxide, into the well adjacent the actuatingelement, traveling valve 30 of pump 24 so that reciprocation of valve 30will intimately mix the solution with the viscous crude oil, includingany water, entering the well from at producing formation. Theemulsion-creating sodium hydroxide solution flows from tank 10 throughline 14 under the control of valve 12 and metering pump 16 injects itinto well tubing 18. The solution then intermixes with the well fluidsabove the discharge side of pump 24 in annulus 20, formed by tubing 18and pipe string 22. At this point crude oil, being lifted by theplunger, or traveling valve, 30 of pump 24, also flows out of slots 26into annulus 20. The reciprocation of plunger 39 then agitates theaqueous hydroxide solution and oil enough to create the desiredoil-in-Water emulsion.

Metering pump 16 supplies the hydroxide solution to tubing 18 at a ratesufficient to form with any native, or formation water entering thewell, an oil-in-water emulsion with a concentration of about 30% to 50%water and about 70% to 50% oil, by volume, based on the emulsion. Loweroil concentrations can, of course, be

used with some additional reduction in viscosity of the produced fluid,if the water cut is even higher. As indicated schematically in FIGURE 1,the viscous crude oil from formation 32 enters the well bore throughslots 34 in liner 36. The intake of pump 24 is through tailpiece 35,formed as slotted tubing, connected to the bottom of conduit 22.

FIGURES 2 and 3 illustrate in greater detail the construction of pump 24and respectively illustrate the pump during an upstroke and a downstrokeof traveling valve 30. As is well understood in pump art, ball 38 oftraveling valve 30, and ball 48 of standing valve 4%), respectively,control the fluid intake and output from pump 24 when rod 17 isreciprocated. As indicated (FIGURE 2), ball 38 lifts off valve seat 39when valve 30 drops in barrel 37 of pump 24 so that fluid trapped inbarrel 37 by ball 48, seated on valve seat 49 rises through centralopening 41 in valve 30. On the upstroke of sucker rod 17 (FIGURE 3),ball 33 seals on valve seat 39 to force oil trapped above ball 38 outthrough slots 26 in tubing 13 to mix in annulus 20 with aqueoushydroxide flowing down tubing 18. At the same time, ball 48 of standingvalve 40 lifts from valve seat 49 to admit additional crude oil. Thecrude oil enters the well from formation 32 through openings 34 in liner36 and slotted liner 35. The lower end of pump 24 is landed on seat 31formed above liner 35 and anchored there by tail stock 33.

Desirably the viscous oil is pumped into annulus 2% by pump 24 throughslots 26 in tubing 18, at a rate suficient to intimately mix it with theaqueous hydroxide solution flowing down tubing 18 and thereby form therequired oil-in-water emulsion.

Alternatively, where the rate of pumping is not high and it is diflicultto mix the basic solution and crude adequately, the basic solution maybe advantageously introduced through valve 82 and line 8% to a pointbelow the pump intake. Line runs down the annular space between casing19 and tubing 22, so that the solution flows into liner 35 to mix withthe production fluids, viscous crude and any water, as they pass throughpump 24. With such an arrangement, obviously internal tubing 18 can beremoved or used for additional flow capacity since the oilin-wateremulsion flowing directly around sticker rod string 17 does notappreciably retard its motion either on the upor down-stroke. Becausethe viscosity of the oil-inwater emulsion is low, the rod string 17drops freely by gravity. Very light hydrocarbon solutions, kerosene orthe like, could be used to reach a similar reduced viscosity 7 but theyseldom are because of the cost. However, even if cost were notconsidered, the resulting dilution does not approach the low viscosityof our oil-in-water emulsion, which can be adjusted to about that ofwater. At this low viscosity the oil-in-water emulsion will containabout 50% oil as the discontinuous phase. The remaining 50% is water, asthe continuous phase.

FIGURE 1 also illustrates one way of automatically controlling theproperties of the oil-in-water emulsion to an optimum degree. As stated,the oil-in-water emulsion contains 50 to 70% oil and 30 to 50% water. Ingeneral, the higher the water content the more fluid or less viscous isthe emulsion. Accordingly, the viscosity of the oilin water emulsion canbe controlled to the desired extent, depending on properties of crudeand water produced by the formation, again sutficient alkaline solutionbeing used to provide a pH of about 8 to 13.8 in the aqueous phase ofthe emulsion. The produced oil-in-water emulsion flows up productiontubing 22 under the hydraulic pressure applied by pump 24 to gauge, orstorage, tank 64 from wellhead 51 through flow line 50. To maintain thequality of the emulsion, two measurements are made on the oil-inwateremulsion flowing through line 50. One of these determines viscosity.Bypass lines 53 and 52 supply a sample through detector 54. The flowrate is similarly measured by orifice 56 and flow rate detector 58. Theviscosity and flow rates, as measured by detectors 54 and 58,respectively, are then used to regulate addition of sodium hydroxidesolution, from tank 10, and any required additional water, from tank 13,to line 14 through valves 12 and 15, respectively, by the operation ofcontroller 60. By proper regulation of valves 12 and 15 an optimumamount of sodium hydroxide of proper concentration can be supplieddownhole through feedline 14 and injection pump 16 into tubing 18.

If desired, emulsion produced from the well is piped directly to storagetank 64 from wellhead 51 by lines 50 and 62. As mentioned above, one ofthe advantages of so doing is that flow resistance through lines 50 and62 is substantially reduced so that power input to downhole pump 24 toforce the production fluid up tubing 22, and through wellhead 51 tostorage tank 64 is also reduced. If it is desirable to break theemulsion before the oil is stored, the emulsion can be fed to emulsionbreaker or treating tank 66 by closing valve 65 in line 62 and openingvalve 67 in line 68. The emulsion can be broken by treatment with saltsand/ or acids or heat. After breaking, oil from the top of tank 66 maybe sent to storage by line 69 under the control of valve 70. The waterphase is disposed of through valve 72 and line 73.

The embodiment of FIGURES 4, S and 6 illustrates application of theinvention to another conventional well pumping system. In thisembodiment, pump 124 is operated hydraulically, rather thanmechanically. As seen in FIGURE 4, pump 124 is supported in the well onpipe 126. Pipe 126 also carries the pressurized actuating fluid whichconventionally is hydraulic oil. However, in accordance with the presentinvention, an aqueous solution of sodium hydroxide, capable of formingthe oil-inwater emulsion is used as the power fluid. Surface hydraulicpump unit 130 driven by engine 132 supplies this aqueous hydroxidesolution from tank 134 and line 136. The discharge of surface pump 130then flows to downhole pump 124 through surface pipe 138 and injectiontubing 126.

FIGURES and 6 illustrate fluid flow through well pump 124. It will beseen that pump 124 engages tailpipe 102 through passage 103 in packer100, so that the pump intake is submerged in the liquid produced by thewell. Tailpipe opening 104 of pump 124 then admits oil to lower, orintake, chamber 105. In this embodiment of our invention, intake chamber105 of pump 124 also serves as a mixing chamber to create the requiredoilin-water emulsion by agitating the crude oil with the aqueonehydroxide solution flowing down hydraulic tubing 126. This solutionreaches chamber through passageway 107 that conducts the discharge fromthe upper, or power section, 110 of pump 124. Power fluid actuatespiston element 112 of power section 110 to drive plunger 114 up and downin pump section 116.

As will be understood by those familiar with hydraulically-operated,oil-well pumps, slide valve 117 alternately reverses connections betweenthe opposite ends of chamber 118 to drive piston 112 down and up asshown by the arrows in FIGURES 5 and 6, respectively. Slide valve 117connects the exhaust from chamber 118 to line 107 so that the aqueoushydroxide solution is continuously supplied under pressure to pumpintake chamber 105. Lower section 116 of pump 124 then pumps theemulsion from discharge ports 120 and 121 to well casing 125 andpipeline 144 for storage in tank 145. The intake ports for pump section116 are indicated to be under the control of check valves 122 and 123.Similar check valves 111 and 113 control the flow out of discharge ports120 and 121, respectively, on alternate strokes of piston, or plunger,114.

The two above specific embodiments illustrate use of the method of thepresent invention in both mechanically actuated and hydraulicallyactuated pumping units. It will be apparent to those skilled in the oilwell pumping art that many other mechanical forms of apparatus can beused to create an oil-in-water emulsion that will reduce the pumpingpower required to lift viscous crude oils. In addition to thealternatives mentioned above it is also known to use hollow sucker rodsfor mechanical pumping systems to drive the downhole pump. In theseunits, a diluent flows down the hollow rod string and discharges intothe tubing just above the pump plunger. The diluent and crude oil mix atthis point. Obviously, in such equipment our aqueous hydroxide solutioncan be substituted, in the same way as in the embodiment of FIGURE 1, toreduce the viscosity of the entire system to about that of water bycreating an oil-in-water emulsion.

As discussed before, some downhole hydraulic pumps operate as a closedsystem. That is, the hydraulic fluid is returned by a separate line tothe power unit, such as pump in FIGURE 4, without loss, by mixing itwith the produced crude oil. By using an aqueous alkali solution, as inthe present invention, the return line can end adjacent the pump tocreate the desired oil-in-water emulsion. If the hydraulic pressure atthe pump discharge is low, it may be desirable to use a nozzle to jetmix the crude oil and aqueous hydroxide solution. The degree of mixingneed not be great, but should at least be suflicient to permit intimatecontact of the viscous crude by the alkaline solution. If desired, andfor somewhat better volume control, a separate line can be used tosupplement or replace the supply of aqueous alkaline solution to thepump intake. For example, in FIGURES 4 to 6 a supply line can be tappedinto tailstock 104. Flow is then controlled by valve 142.

In creating the desired oil-in-water emulsion downhole, it is importantthat the base be present in such concentration as to ensure theformation of a stable oil-in-water emulsion. At too low concentrationsthe emulsion is difficulty formed, and unless an oil-in-water emulsionis formed, the advantages of the present invention cannot be obtained.High concentrations tend to invert the emulsion, forming water-in-oilemulsions that frequently have greater viscosity than the oil alone.

The method of the present invention was used to increase the pumping ofan oil well in a California field delivering a producing streamcontaining about 300 barrels of oil and 45 barrels of water per day. Atstandard temperature and pressure the produced stream of water and oilhad a viscosity 0 fover 200,000 centipoises. The subject well prior toconversion to the present method was being pumped through a systemsomewhat similar to that of FIGURES 1 to 3. The sucker-rods were hollow9 and a hydrocarbon diluent, Railroad Diesel of 31 API gravity, wasadded at a rate of 24 barrels per day. The diluent discharged into thesurrounding tubing just above the pump plunger.

The production tubing in the well had an IJD. of 4 inches and the pumpwas set at a depth of 1530 feet. The stroke of the sucker-rod string was10 feet and the power available gave a maximum pump rate of 4 strokesper minute. The fluid level in the well stood at about 350 feet from theearths surface so that the pump was submerged about 1200 feet. The flowline from the wellhead to the gauge tank was 1640 feet long and was also4 inch I.D. pipe.

To perform the method of this invention, an auxiliary pump was used topump a 0.10 N aqueous solution of sodium hydroxide down the hollowsucker rod string. The solution Was made up using soft, fresh wateravailable at the well site. Using the produced crude, prior toconverting from hydrocarbon diluent to sodium hydroxide solution,several oil-in-water emulsions were prepared at the wellhead using saidsolution to establish that stable oil-in-water emulsions could be madewith the fluid then being produced.

A two-hour production run was then made of the well with the pumpadjusted to 3 strokes per minute. The well produced at a net daily rateof 160 barrels of oil and 40 barrels of emulsified water, but with nofree water production observed. (Hydrocarbon diluent volume of 24barrels was subtracted.) The flow line pressure at the wellhead was 160p.s.i.g., with production being discharged at atmospheric pressure to agauge tank.

The auxiliary pump used to supply sodium hydroxide solution was thenconnected and the solution substituted for the hydrocarbon diluent. Itwas supplied to the hollow sucker-rod string at a rate of 100 barrelsper day. The hydraulic pumping unit was maintained at a rate of 3strokes per minute. In 35 minutes an oil-in-water emulsion appeared atthe wellhead, the emulsion having a pH about 9. Ten minutes later theoil-in-water emulsion reached the gauge tank. The wellhead pressure inthe flow line decreased to 10 p.s.i. (a drop of 150 p.s.i.).

With the pump unit still maintaining 3 strokes per minute, however, thewellhead sample changed from an oil-in-Water emulsion to a creamy,smooth water-in-oil emulsion after another 20 minutes. The flow linepres sure also increased to 140 p.s.i., indicating that additional saltWater was entering the well and inverting the emulsion. Forty minuteslater the oil production sampled from a valve at the well-head was notedto have a rope-like consistency, and contained some free water. Thewater was brownish in color, indicatingv slight emulsification, orextraction of colored material from the oil. Ten minutes later the flowline pressure again reduced to p.s.i. A gauge of fluid production on theabove conditions for two hours indicated fluid production was at therate of 470 barrels per day. Subtracting the 100 barrels per day aqueoushydroxide injection, the net yield of the well was 370 barrels per day;an increase of 170 barrels per day, or an 85% increase over previousfluid production from the well. Net oil produced was at a rate of 220barrels per day.

A review of the results of the above run indicates that the backpressure on the pump is reduced by reducing viscosity of the fluid inthe tubing and flow lines. This back pressure reduction increased pumpefliciency. The sucker-rod string dropped freely so that the full strokeof the surface unit was transmitted to the pump; this also contributedto the increased pump efliciency. Thus, essentially the only load on thepump was the weight of the sucker-rod string and the hydrostatic headrequired to lift the fluid from its level in the well to the earthssurface, a total of 350 feet.

If the weight of the sucker-rod string, less buoyancy, and thehydrostatic head of 350 feet are subtracted, the

lifting force on the sucker-rod at the start of the pump stroke was 3250pounds and 4350 at the end of the stroke while crude plus hydrocarbondiluent was being pumped. When the oil-in-water emulsion was pumped,lifting force varied from to 950 pounds during the pump stroke. If crudehad been pumped without diluent, the lifting force would have beenconsiderably higher than with the hydrocarbon diluent. Thus, the effectof pumping oil-in-water emulsion is even greater than the comparisonbetween emulsion and hydrocarbon diluted crude.

Emulsions of the oil-in-water type created by downhole pumping, asdisclosed by this invention, can be broken to their constituent oil andwater phases by treating with salts and/ or acids. Examples of salts aresodium chloride, ammonium chloride and calcium chloride. Thus, brine orsea water can be used. In the event acids are used, the acid, forexample, hydrochloric, sulfuric or carbonic, can be added to theemulsion in proportions up to the chemically equivalent amount of baseadded in forming the emulsion.

In accordance with another form of the invention, a nonionic surfactantsolution is used to form the oil-inwater emulsion. Apparatus such asillustrated in FIG- URES 15 is also useful in this embodiment. All thatis required, for example, in the setup illustrated in FIGURE 1 is toreplace the source 10 of sodium hydroxide with a source of a suitablenonionic surfactant. In a similar manner, the source of caustic solutionstorage in FIGURE 4 is replaced by a suitable source of surfactantsolution.

The oil-in-water emulsion may be formed with as little as 15% surfactantsolution. It is preferred, however, to have substantially moresurfactant solution present in the well when forming the emulsion. A50/50 ratio of surfactant solution and oil has given good results.

As indicated above, the upper oil/ water ratio is limited by the amountof water needed to produce a suitable oil-in-water emulsion for pumping.The upper limit for oil in most surfactant and crude oil mixtures isabout 85 percent. Thus the minimum amount of water that can be used inaccordance with the present invention usually is about 15 percent. It ispreferred, however, to have excess water available to insure thatinversion of the emulsion will not occur. Inversion of the emulsion to awater-in-oil emulsion is extremely undesirable since water-in-oilemulsions are very viscous.

An aqueous surfactant solution is added to the oil to form the desiredmixture. As indicated, the amount of water may be as little as about 15percent. The surfactant is added to the water before the water is mixedwith the oil. Nonionic surfactants useful in the present invention canbe divided into five basic types by linkage. (See Emulsion Theory andPractice, by P. Becher, ACS Monograph, No. 162, 1965, ReinholdPublishers, New York.) These five types are ether linkage, esterlinkage, amide linkage, miscellaneous linkage and multiple linkage. Theether linkage, nonionic surfactants are preferred for use in the presentinvention. The surfactants preferred for use in the present inventionare selected from the group having the general formulas:

where R, R and R =any hydrocarbon group and 11 and n =4 to 100.

As indicated above, other surfactants, such as the ester A list ofhighly preferred surfactants is set out below: linkage and the amidelinkage, may be used in accord- TABLE I ance with the invention. Thegeneral formula for the e N ester linkage is: lopuet-ary ame R 11 NI?CmHzs 14 (Ii infiifoo 430 6 1 4 R-C-O-(CHzCHgOLJI IQEPAL CO 6 whereR=any hydrocarbon group and 77:4 to 100. fa s The general formula forthe amide linkage surfactant IGEPAL CO 730 1 IGEPAL 00 350.

(11x5, 000. 100 if (CHQGH'OMH 710. 10 11 Gal )1 070. 50 R C O N DMEPrtgniet-arl lnuixturo,

n c eiuica ysimilar (CHZCHZO) to IGEPAL co 887. where R=any hydrocarbongroup and 77 and 77 :4 to "Su1table ester l1nl age surfactants, forexample, mclude surfactants h v'n th own r o The hlghly preferrednonlonic surfactants for use in aca 1 g 6 011 1 g gene a] f rmulascordance with the invention are the nonylphenoxypoly H (e thyleneoxy)ethanols. Superror results have been 011- 20 CHH% C O (CEHUOG) (CZH4O)4Htamed W1th surfactants contammg l0l5 moles ethylene oxide per mole ofnonylphenol. These surfactants have decreasing water solubility withincreasing temperature. Cum?C O (CflHnOGPWZHHOMOH Emuls1ons formed w1ththese types of surfactants have good stability up to 160 F. and fairstability in the 160- h 175 F. range. At temperatures in the 200 F.range, sep- 0,,H 0 c 1, 11 Manon g 011 Watter 2 53 'i ii i Table II setsout the results of a number of demonf use a OW Wa er i g actan 8 Opera 6a strations showing various combinations of oil/water rag s i s a 1 t dfr tios, surfactants, and surfactant percentages useful in h Y li are lf 1 are 56 69 e Om a forming transportable emulsions in accordance withthis group avmgt e genera 0mm invention. The results show that suitablemixtures may R O OH CH O) H be formed with water containing .05 percentsurfactant 2 2 based on added water. It is usually preferred, however,and to form the mixture with at least about .1 percent surfactant basedon added water. The advantage that is obtained by forming thetransportable mixture is readily seen in the case of Boscan crude. Theviscosity of pure Boscan crude is 80,000 centipoises at 70 F. However,the viscosity of an emulsion containing 75 percent Boscan R2 and 25percent Water is only centipoises at P. where R, R and R =any alkylradical and where 77:4 Table II shows properties of various mixtures ofBoscan to 100. crude, water and surfactants.

TABLE 11 Chemical Mixture Viscosity Water Sample. No. Oil/WaterRemaining in Ratio Namo Vol. percent in F. Cps. Oil Separated Water at200 l.,

percent 25 C0 710 0.10 117 03 11.7 75 25 00 710 0.10 112 7 2. 0 75/25 CA530 0.10 115 55 10.8 75/25 CA 030 0.10 103 07 2. 0 75/25 DM 970 0. 10121 00 12.5 75/25 DM 970 0. 10 10s 00 2. 4 75 25 DME 0. 10 109 91 10. 575/25 DME 0. 10 104 3. 0 75/25 NIW 0. 10 120 50 75/25 NIW 0. 10 122 5510. 0 75/25 NIW 0. 10 110 45 2. 1 30 20 NIW 0. 10 127 40 30/20 NIW 0.1043 10 0 75/25 NIW 0. 05 11s 11 75/25 NIW 0. 05 120 43 10. 3 30 20 NIW 0.05 123 25 11. 0 35 15 NIW 0. 05 30 20 00 710 0.10 123 07 10.2 75/25 00730 0.10 115 92 s. 0 80/20 00 730 0.10 110 147 3. 0 75/25 CO 350 0.10110 142 11. 0 80/20 C0 850 0.10 111 137 12. 0 75/25 CO 887 0.10 112 10212.0 80/20 CO 837 0.10 117 133 11.0 75/25 CO 435 0.10 103 104 3. 7 80/2000 430 0.10 117 11. 0 30/20 CA 530 0. 10 110 48 s. 0 75/25 DM 710 0. 10120 04 9. 0 30 20 DM 710 0. 10 120 55 10. 5 80/20 DM 070 0. 10 115 93 0.7 80/20 DME 0.10 114 11. 0 75/25 NIW 0. 15 110 03 11.0 75/25 NIW 0. 20117 72 15. 0 75/25 Visco-llll 0. 20 114 45 75/25 vim-1111 0. 30 105 81isco-llll 0. 05 751 5 $11, 111 3,85 s 45 iscol 5 75/2" {10 730 10 1m 95t 1 '13504111 0.05 75125 CO 8 M5 114 30 The advantages of the method ofthe present invention have been demonstrated with a number of othercrude oils. TAB LE W Table III sets out the properties of mixturesprepared I Water Wet -Q Dispersedin with California crude oils utilizingfresh water and vari- Olw Glass Wall dummy Water Toluene oussurfactants. The California crude oils are namely in- Y N dicated as A,B and C. The A crude has an API gravity es '1 31 of 12.17 and aviscosity of 14,000 centipoises at 70 F. fi The B crude has an APIgravity of 12.17 and a viscosity I YZg, of 19,000 centipoises at 70 F.The C crude has an API gravity of 10.15 and a viscosity of 70,000centipoises at The data given in Tables V and VI indicate that the 70 F.upper limit for oil in most aqueous solution, crude oil TABLE IIIChemical Emulsion Viscosity Producing Oil/Water Chemical ConcentrationZone Ratio in Water, Temperature, Viscosity,

Volume percent F. cps.

99. 9. 9. 99 HD-IHHHHHHH QOOQQOOOQ In Table IV, the properties ofmixtures prepared with mixtures is about 85 percent in order to form asuitable the California crudes nominated A, B and C with aqueous mixturefor pumping. solutions containing IGEPAL CO 850 are shown. As indi- Ithas been found that the water with which the mixcated in the table, themixture is prepared with both fresh tures of the present invention areformed is not limited and produced waters. Suitable mixtures were formedwith to distilled or potable water. The nonionic surfactants are 0.04%surfactant. not aliected by salts in solution in the water; and, there-'IABLE IV Chemical Emulsion Viscosity Producing Oil/Water WaterConcentration Zone Ratio in Water, Temperature, Viscosity,

Volume percent F. cps.

75/25 Prodiuced As is evident from the data presented in Tables II, HIfore, formation water, and even seawater, can be used in and IV, atremendous improvement in viscosity can be forming the mixtures inaccordance with the present invenobtained by forming transportableemulsions of the vistion. This is a particularly desirable feature infield 0pcous crudes in accordance with the present invention. erationssince it may not be economical to obtain large T bl V b l shows th ff tf gradually decreasing quantities of relatively fresh water for use inthe process the water content in the aqueous surfactant mixture. The theeelmate Writer in the Well y have high Salt d 11 d i T bl V was aCalifornia rude t A tent. Table VII sets out the properties of a Boscancrude, oil maintained at 140 F. A 0.1 percent IGEPAL CO 850 aqueoussurfactant mixture when the water utilized was in tap water at 72 F.formed the aqueous solution. It is 100 percent Seawaten TWO emulsionswere p p with apparent h t i1-in.watr emulsions were f d t h 0 differentsurfactants and with seawater obtained directly 75/25 to the 15 mixturesbecause the mixtures were ffem the Oeean at Huntington Beach, Califwaterwet and had electrical conductivity.

TABLE VII TABLE V A B Water Wet Elect. Con- Dispersed in 65 O/W GlassWall ductivity Ratio 75/ 5 75/25 Water Toluene Oil Temperature, F 140Seawater Temperature, 50 41 Surfactant C0 730 Visco 1111 SurfactantConcentration in Seawater,

Volume Percent 0.1 0.1 Dispersed in Water Yes Yes 70 ConductedElectricity Yes Yes EmulsionViscosity (cps. at 98 F.) 183 Under 200Table VI below shows the effect of varying the oil/ water 8 Afterstanding at for no Hour, Volume Percent Water ratio 1n mixtures ofCalifornia crude 011 D. The D crude Remaining in Crude as was at atemperature of F. and was mixed with an aqueous surfactant solutionformed of 0.1 percent DM In a demonstration conducted to show theadvantages 970 at 72 F. 75 of this aspect of the present invention, anonionic sur- 15 factant was added to a producing well in the HuntingtonBeach Field in California. The nonionic surfactant was IGEPAL CO 850 andhas the general formula:

Where R=C H and 11:20.

The well originally was producing 13 barrels of oil and 15 barrels ofwater per day. The well was completed in three producing Zones with theoperating fluid level covering only the bottom zone. The nonionicsurfactant was added to the annulus between a producing string and thecasing. The surfactant was mixed with water at the surface for injectionin the annulus. One-tenth of a pound of surfactant per barrel of oilproduced was added to the well. Thus, when the well was producing 13barrels of oil per day, 1.3 pounds of surfactant was used. This dailyamount of surfactant was mixed with from 2 /2 to 5 barrels of water fordaily injection. The surfactant solution was metered into the well overa 24 hour period. As indicated above, the oil production withoutsurfactant was 13 barrels of oil per day and 15 barrels of water. Withthe surfactant added to the well, 14 barrels of oil per day and barrelsof water per day were produced. The major improvement, however, occurredin improving the efiicien-cy with which the oil was produced. Forexample, the pressure drop in the 900 feet of 2 /2 inch tubing in thewell was 800 psi. before the surfactant was added. The pressure drop inthe line after the addition of surfactant, was reduced to only 5 p.s.i.The polished rod horsepower prior to the addition of surfactant was 3horsepower and after the addition of surfactant was only 2 horsepower.The peak torque prior to the addition of surfactant was 55,000 in-ch/pounds and with surfactant, was reduced to 30,000 inch/pounds. Downholepump efficiency without surfactant was 47% and with surfactant was 60%.In addition, the use of surfactant caused the fluid level over the pumpto be reduced from 600 feet to 300 feet. The surfactant also had amarked effect on the process of rod drop. The frictional drag on thepump rod during downstroke was reduced to the original drag by the useof surfactant. The above figures indicate that wells utilizing themethod of the present invention can be handled with smaller pumpingunits and lighter rod strings. It is also expected that oil recoverywill be improved due to the lowering of the fluid level in the well.

While certain preferred embodiments of the invention have beenspecifically disclosed, it should be understood that the invention isnot limited thereto as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claims.

We claim:

1. In the method of pumping viscous crude from a well bore by a downholepump in said well bore, the improvement of increasing the pumpa'bilityof said viscous crude, which comprises forming adjacent said pump anoil-inwater emulsion of said crude, said oil-in-water emulsion having asubstantially lower viscosity than the unemulsified viscous crude, andpumping said oil-in-water emulsion from said well bore.

2. The method of claim 1 further characterized in that the emulsion isformed by adding a nonionic surfactant to the well.

3. The method of claim 2 where the surfactant is selected from the groupconsisting of 16 and R1 O-o-wmcmonga where R, R and R =any hydrocarbongroup and n and n. =4 to 100.

4. The method of claim 1, wherein the aqueous phase of the emulsion hasa pH in "about the range 8 to 13.8.

5. The method of claim 4, wherein the emulsion contains, by volume,about 50 to oil, and 30 to 50% water, based on the emulsion.

6. The method of claim 5, wherein the base is an alkali metal hydroxideor ammonium hydroxide.

7. The method of claim 5, wherein the base is sodium hydroxide.

8. The method of increasing the rate at which a viscous asphaltic crudecan be produced from a formation traversed by a well bore provided witha downhole pump, which comprises introducing an aqueous basic solutioninto said well bore at a point adjacent to the actuating element of saidpump to neutralize the saponifiable constituents of said crude to a pHin about the range 8 to 13.8 and to convert said viscous crude into anoil-inwater emulsion, the water introduced by the basic solution and anyconnate water being sufiicient to produce an oil-in-water emulsionhaving a substantially lower viscosity than the unemulsified crude oil,and then pumping said emulsion from said well bore at a higher rate thanis possible using the same power input to said pump to produce untreatedquantities of viscous crude.

9. The method of claim 8 in which the aqueous phase of the emulsion hasa pH in about the range 9 to 10.

10. The method of claim 9, wherein the emulsion contains, by volume, 50to 70% oil, and 30 to 50% water.

11. The method of claim 10, wherein the base is an alkali metalhydroxide or ammonium hydroxide.

112. The method of increasing the rate of pumping a viscous parafiiniccrude from a well bore provided with a downhole pump, which comprisescontacting the crude adjacent the pump with an emulsifying agent, water,and a base, emulsifying said crude into an oil-in-water emulsion, saidoil-in-Water emulsion containing by volume, 50 to 70% oil and 30 to 50%water, based on the emulsion, maintaining a pH in the aqueous phase ofsaid emulsion in about the range 8 to 13.8, and then pumping saidemulsion from the well bore to the surface.

13. The method of claim 12 wherein the base is an alkali metal hydroxideor ammonium hydroTide.

14. The method of claim 13 wherein the emulsifying agent is derived fromnaphthenic acids having an average molecular weight in about the range300-700.

15. The method of claim 14 wherein the base is sodium hydroxide.

16. The method of claim 13, wherein the emulsifying agent is the alkalimetal extract of an asphaltic crude.

References Cited UNITED STATES PATENTS 2,530,673 11/1950 Zinszer 166-453,073,387 1/ 1963 Dunning et a1. 16645 3,120,266 2/1964 Martin et al.16645 X 3,196,947 7/ 1965 Van Poolen 16645 ERNEST R. PURSER, PrimaryExaminer.

